Two-wire multiple automatic telephone system.



C. L. GOODRUM.

TWO WIRE MULTIPLE AUTOMATIC TELEPHONE SYSTEM. APPLICATION FILED JUNE 21. 1915.

1,251,503. Patented Jan. 1, 1918.

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TWO WIRE MULTIPLE AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED JUNE 21, I915- Patent ed 32111.1, 1918.

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TWO Wl-RE MULTIPLE AUTOMATIC TELEPHONE SYSTEM.-

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APPLICATION FILED JUNE 21, I915.

Patented Jan. 1, 1918.

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UNITED STATES PA canton.

CHARLES GOODRUIVI, OF NEW YORK, N. Y., ASSIGNOR, BY MESNE ASSIGNMENTS, TO \VESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK.

TWO-WIRE MULTIPLE AUTOMATIC TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Jan. 1, 1918.

Application filed June 21, 1915. Serial No. 35,326.

To all whom it may concern:

Be it known that I, CHARLES L. GoonRUM, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Two-\Vire Multiple Automatic Telephone Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone systems, and particularly to systems in which the talking connection from the calling to the called subscriber is established by means of automatic or mechanically controlled switching devices.

One of the features of this invention resides in the provision of a controlling relay or relays common to a group of lines which are arranged to control the operation of any one of a group of switches which has access to the lines of the group.

Another feature of the invention resides in the provision of a line finding switch having but two terminals individual to each line terminating thereat, and two brushes which are adapted to pass over and test the contacts in the bank of subscribers line terminals while searching for a calling line, without producing a material electrical disturbance of the busy lines of the group which are passed over.

A further feature of the invention, which is incidental to the one just referred to, is the provision of a test relay common to a group of lines arranged to be associated with one side of a calling subscribers talking circuit.

Another feature of the invention resides in the provision, in an automatic system employing central or common battery, of two-wire multiple selector and connector switches, (that is, switches which employ but two fixed contacts for each circuit or line) and means for testing busy lines without causing a material electrical disturbance of the lines tested.

Another feature of the invention resides in the provision of means for controlling the release of certain of the automatic switches by altering the electrical condition of a portion of the talking circuit which is inductively connected to the rest of said circuit but is non-conductively joined thereto. v 1

A still furthervfeature of the invention resides in release controlling means such that, upon the operation of a release magnet, the line or trunk will be instantaneously rendered idle or selectable, means being provided for positively maintaining the release magnet energized until the switch has returned to its normal position. 7

In the drawings, Figures 1, 2 and 3, with Fig. 1 at the left and Figs. 2 and 3following in order, show the circuits employed in the system, and diagrammatically represent the switches and circuit controlling devices used therewith. Fig. a} shows a modification of the circuits shown in Fig. l.

Any step-by-step two-movement switch maybe employed with the circuits shown. A switch of this general character is shown in patent to Keith & Erickson No. 815,176, although a switch such as disclosed in applicants patent 1,231,013, June 26, 1917, will preferably be employed. Of course, it is to be understood however that with'this invention only two brushes will be employed on the switch, and the stationary contacts will be correspondingly reduced in number. Although the features of the invention are disclosed in a system using step-by-step switches, it is equally applicable to systems employing other types, as power driven switches.

With each switch is associated a circuit changing device for controlling the operating circuits of its respective switch. These devices may be of the general character of the switch which is shown in the above mentioned patent and referred to as a side switch. The switch shown in said patent, however, will not operate in the manner necessary to fulfil the requirements of the present invention. A circuit controlling switch, such as will be employed in the present invention, is shown in applicants patent previously referred to. This switch may be caused to operate at any stage upon the energization instead of upon the dee ergization of its magnet, merely by omitting a corresponding tooth from its escapement ratchet.

Referring to the drawings, each line finder switch preferably includes 100 sets or pairs of contacts representing the terminals of incoming subscribers lines. These contacts and the corresponding subscribers lines will be arranged in groups preferably of ten each. Associated with each group of subscribers lines are the circuit controlling devices illustrated in the dotted rectangle at the lower left-hand corner of Fig. 1. Normally associated with each group of lines is a finder switch and a starter wire is employed whereby, if the switch normally allotted to the lines of the group is busy, the starting circuit will be continued to the switch which is normally allotted to the next group, and if this one be busy, to the next, and so on. Thus any line in the major group of subscribers lines having terminals multiplied to the switches of the group may be selected by any one of the finder switches of the group.

It is thought that now the invention will be readily understood from a description of the operation of extending a call from the subscribers station, shown in Fig. 1, through to the subscribers line illustrated at the right in Fig. 3.

Assuming that the subscriber at the left in Fig. 1 removes his receiver from the book, a circuit is completed in the usual manner through the windings of the line relay 1, which is energized and completes a circuit from grounded battery, through relay 2, left back contact of relay 3, left back contact of test relay 4, left front contact of relay 1, and right back contact of relay 4 to ground. Relay 2 is energized and completes at its left armature a short-circuit of the left armature and contact of relay 3. At the front contact of its outermost right armature, it completes a circuit from ground, through the right armature of relay 4: to the group test contacts 5 of the line finder switches. At its front contact and innermost armature, it completes a circuit from ground through the right armature of relay 4, relay 3 to starter wire 6. If the switch, which is normally associated with the group of the calling line, is idle, the wiper 7 of the side switch will be resting on the contact associated with the individual interrupting device 8 of the rotary stepping magnet 9. This interrupting device may be of any character in which the stepping magnet interrupts its own circuit when it has completed its forward movement. An arrangement of this general character is shown in Patent No. 831,875, and is also disclosed in my Patent 1,281,013 above mentioned.

Assuming that the switch normally allotted to the calling subscribers group is idle, group selection of the switch will take place through the repeated energization and cleenergization of the stepping magnet 9. lVhen the group hunting test brush 10 of the switch engages the contact 5, corresponding to the group of the calling subscriber, a circuit ill be completed from groimded battery through the escapement or side switch magnet 11. switch wiper 12, brush 10, to contact 5 which has been grounded by the energization of relay 2. The escapement magnet, which in this case acts as a test magnet, is energized, and by means of the peculiar structure of the side switch, such as illustrated in my copending application, the side switch wipers 7, 12, 13 and 1 1 immediately move to their second position.

Had the switch normally associated with the calling line group been already employed, the side switch wiper 7 would'have been in its third position, and the starter wire 6 would have been continued through wire 15 to the switch of the next group of lines, as through a wire correspoi'iding to 15' shown at the lower left-hand corner of Fig. 1. If that switch should be busy, its side switch wiper 7 would also be in its third position, and the starter wire would be similarly extended on to the switch of the next group, and so on.

The escapement magnet 11 having operated, and the controlling switch wipers having moved to position 2, a circuit is now completed from battery, through the stepping magnet 16 and its individual interrupter 17, side switch wiper 7, wire 6, relay 3, innermost armature and front contact of relay 2, and right armature of relay i to ground. The switch now hunts over the terminals of the lines in the group of the calling subscriber. It may be noted that with the line relay energized, a circuit is completed from ground, through the alternating current generator 18, test relay 4, right front contact of relay 1 to the upper side of the line. At this time the controlling switch w'per 1% is in engagement with contact 19. Thus, when the switch brush 20 engages the line terminal 21 of the calling line, a circuit will be completed from said alternating generator 18, through the test relay a, line terminal 21, brush 20, wiper 14, contact 19, condenser 22, and resistance 23 to battery. Relay at will thus receive an energizing impulse of current, and at its right armature will interrupt the circuit for the escapement magnet 11 and the stepping magnet 16.

Magnet 11 in deenergizing will more the wipers 7, 12, 13 and 1 1 to their third pos tion. The starter wire (3 will now be joined to the starter wire extension 15 through wiper 7 Wiper 13, in moving into its third posi tion, will. complete a circuit from battery, through resistance brush and contact engaged thereby, and in the cutofi relay 2% to ground. Relay 2% will be energized, thus cutting off the line relay 1. Relay 4 was deenergized when wiper 14: moved from contact 19, and relay 2 is pre- 28, the lower switch vented from being again energized by the immediate falling off of the armatures of relay 1.

The arrangement which makes it practical to use stationary contacts embodied in the talking circuits of the subscribers lines as test contacts is the feature of connecting the test relay to said contact instead'of associating the test relay with the movable contact of the finder switch, as has formerly been the practice.

The inclusion in .the circuit of the test brush of a high resistance or condenser operates to make the circuit of said brush practically opaque to current of the characteristics which would be upon the to illllldlS of the busy lines tested so no material disturbance would be produced on said lines.

Associating the test relay with the stationary contact of the calling line also insures that no false test will be made, as it is impossible to complete a circuit for said relay except when the brushes of the finder switch engage the contacts of the calling line. This relay, it may be noted, is common to a group of ten lines, and may control the testing operation of any one ofv the group of switches which are arranged to make connections to the subscriber lines in the group.

The calling subscribers line is now extended through to the side or controlling switch wipers of the selector switch. shown at the left in Fig. 2 of the drawings. The calling subscriber may send, by means of his calling dial, the group selecting impulses to the first selector. V

This calling dial may be of any desired construction, which operates to cause a series of momentary interruptions of the line circuit. Upon the operation of the dial at the calling subscriliers station a circuit is completed from grounded battery through resistance 23, wiper 13, the lower switch brush, front contact and left armature of cutoff relay Zl. the substation apparatus, the substation interrupter, back ver the other side of the subscribers line, right armature and front contact of relay 2%, brush 20, wiper ll, wiper 25 and its first contact, and trunk line or stepping relay '26 to ground. Upon the first energization of relay 26. a circuit is completed from grounded battery, through slow release relay 27, front contact of relay 26 and back contact of relay 28, to ground. delay 2-7 pulls up and does not fall back in the brief interval between the impulses of the series. Upon the first deenergization of relay 26, a circuit is completed from battery through slow release relay 29, left front contact of relay 27 and back cont-act of relay 26 to ground, through the armature of relay delay 29 is energized and likewise holds up during the sending of the series of impulses. Relay 25, 32, 33 and 3st into armature of testrelay 28.

26, at its back contact, also completed a circuit from grounded battery through the group stepping magnet 30 of the first selector. Stepping magnet 30 will be repeatedly energized and deenergized, thus movingthe brushes of the switch into a position to traverse the contacts of the desired group of trunks.

Upon the termination of the series of impulses, relay 26 will remain energized, thus opening up the circuit for stepping magnet 30 and slow release relay 2 When relay 29 was energized it completed an energizing circuit from grounded battery through escapement magnet 31. Now, upon the deenergization of relay 29, the circuit for magnet 31 is interrupted and the magnet becomes deenergized, moving the side switch wipers their second position.

The side switch of the selectors and of the connector operate in a manner slightly different from that which is associated ith the finuer switches, in that the wipers are not moved to their second position upon the first energization of their controlling or escapement magnet.

The wiper 3%, in moving to position 2,

completed a circuit from grounded battery through the stepping magnet 35, its individual interrupter 36, front contact and armature of relay 26, to ground through the The switch brushes 37 and 38 are now automatically moved step by step over the contacts of the trunks in the selected group. The contacts of busy trunks will be supplied with battery potential through relays corresponding to relay 42, so test relay 23 will not be actuated. /Vhen, however, the brushes engage the contacts of an idle trunk, a circuit will be completed from grounded battery, through test relay 28, brush 38, side switch wiper 39 of the second selector (shown at une right of Fig. :2), back contact of inner left armature of relay ellrback contact and armature of relay ll, and back contact and armature of test relay 4.2 to ground. Belay 28 is thereupon energized and interrupts at its back contact the circuit of the stepping magnet 35. and at its front contact completes a circuit from battery through escapement magnet 31, front contact and right armature of slow release rc 9.7 to ground through the armature of reh y 28. The energization of magnet 31 causes the side switch wipers of the first selector to m re to position 3. A circuit is now completed from grounded battery, through resistance 23, over the lower side of the line through substation apparatus, back over the upper side of the line to the side switch wiper of the second selector, and through relay ii to ground. Relay 4:1, in pulling up its armature, interrupts the circuit for relay 28, the armature of which falls off. Thus relays 26 and 28 will be deenergized at substantially the same moment, and as relay 27 is slow to release, its right armature will not engage its back contact until after the armature of relay 28 has left its front contact, thus preventing a circuit from being completed for release magnet 44 through side switch wiper 33 in its third position.

Upon the energization of relay 41 a circuit is completed from grounded battery, through slow release relay 40, front contact of relay 41, and back contact of relay 42 to ground. Relay 40 is energized.

The subscriber now operates the substation dial to send the second series of impulses. With each operation of the interrupter controlled by the calling dial, the circuit just traced through relay 41 is broken, causing said relay t be de'e'nergized and energized once for each interruption of the series. ll ith the first deenergization of relay 41, a circuit is completed from grounded battery through slow release relay 45, innermost left armature and front contact of relay 40, back contact of relay 41, and armature of relay 42 to ground. Relay 45 is energized and completes an energizing circuit for the controlling switch escapement magnet 46. The side switch wipers, however, are not moved by this energization. At each deenergization of relay 41, a circuit is completed for the group selecting stepping magnet 47 in parallel with relay 45, causing the switch wipers 48 and 49 to be stepped from group to group of the trunk terminals until they are in a position to traverse the group of desired trunks.

Upon the termination of the second series of impulses, the relay 41 will remain energized, thus holding open the circuit for the stepping magnet 47 and also for the slow release relay 45. Relay 45 in falling off opens the circuit of the escapement magnet 46 and the side switch wipers are moved to their second position.

A circuit now extends from grounded battery through stepping magnet 50, its interrupter 51, side switch wiper 53, front contact of relay 41, and back contact of test relay 42 to ground. The switch brushes now traverse the terminals of the trunks in the selected group in search of an idle connector switch. lVhen a trunk terminating in an idle connector is reached, a circuit is completed from grounded battery through test relay 42, brush 49, lower conductor of the trunk, left armature and back contact of relay 54 at the connector (Fig. 3), right armature and back contact of slow release relay 55, and back contact of trunk line relay 56 to ground. Relay 42 is energized and interrupts the circuit for the stepping magnet '50 and the slow release relay 40. Relay 42 at its front contact completes a circuit from grounded battery through side switch escapement magnet 46, right front contact and armature of relay 40, to ground.

The side switch wipers are now moved to the third position, whereupon a circuit is completed from battery through resistance 23 over the lower side of the line, through the substation apparatus over the upper side of the line, to ground through line relay 56 at the connector. Relay 56 is energized and breaks the circuit for relay 42 which falls 05. As relay 40 is made slow to release, it has'not yet closed its back contact, and therefore the circuit of release magnet 57 is open. Upon the energization of relay 56, a circuit is completed for slow release relay The apparatus is now ready for the transmission of theseries of impulses for selecting the group of the wanted subscriber at the final switch or connector. The calling subscriber now sends the tens or group series of impulses, causing the repeated energization and deenergization of line relay 56. Upon the first deen'ergization of said relay a circuit is completed from grounded battery through group selecting stepping relay 58, side switch wiper 59, outermost right armature and contact of relay 60, right armature and front contact of relay 55, and back contact and armature of relay 56 to ground. As a result of the repeated energization and deenergization of relay 56, stepping magnet 58 operates to move the switch brushes 61, 62 into a position to traverse the group of switch terminals in which the wanted subscribers line terminates.

Upon the first deenergization of relay '56, an energizing circuit was completed for relay 63 through the front contact of relay 55, and as this relay is made slow to release, it holds up during the series of impulses. The energization of relay 68 resulted in the energization of side switch escapement magnet 64, which, however, is without effect. Upon the termination of the series of impulses and the continued energization of relay 56, relay 63 falls off and opens the circuit for escapement magnet 64 which, in retracting its armature, moves the side switch wipers into their second position.

The final or units series of impulses are 1 now transmitted by the calling subscriber. This series of impulses acts exactly as the preceding one except that side switch wiper 59 has moved to its second position, and consequently stepping magnet 65 is energized instead of the group stepping magnet 58. Under the control of the final series of impulses, the brushes 61 and 62 are moved into engagement with the contacts of the wanted subscribers line. Upon the termination of the series of impulses, the relay 63 is deenergized as before, and in falling ofi completes a circuit through test relay 60.

We will first assume that the called lineis idle. When the armaturecf relay 6311s .re-

tracted, it completes a circuit from ground, through its back contact, armature and contact of escapement magnet 64 (which is not yet retracted), test relay 60, side switch wiper 66 and brush 62 to the lower terminal of the line of the called subscriber. As the called line is idle, ground potential will be on the terminal engaged by brush 62 by reason of the cut-off relay 24:. Therefore, relay 60 will not be actuated as this circuit runs from ground to ground. The circuit of the escapement magnet will thus remain open, and it will retract its armature causing its wipers to move to position 3.

A circuit is now completed from battery through ringing relay 67 side switch wiper 66, brush 62 and cutofi relay 24 to ground. Both relays are energized. Relay 2% operates to isolate the line of the called subscriber, and battery potential is applied to the lower terminal of the line through relay 67 to cause the said line to test busy.

Relay 67 in pulling up completes a circuit from a source of ringing current through ringing trip relay 68, front contact of relay 67, side switch wiper 69, switch brush 61, over the line and through the bell at the substation, and back over the other side of the line to ground through relay 24. Upon the response of the called subscriber, the increased flow of current through trip magnet 68 causes it to pull up its armature.

.V hen the side switch moved to its third position, an energizing circuit was completed from battery through escapement magnet 6%, side switch wiper 70 and its third contact, back contact of relay 68 and front contact of relay 55. The attraction of the armature of relay 68 interrupts this circuit and the side switch moves into position 4, completing the circuit through for conversation.

Talking current is now supplied to the calling subscriber from battery through resistance 23 on the lower side of the line, and to ground through line relay 56 at the connector on the other side of the line. Talking current is supplied to the called subscriber from battery through relay 67 on one side of the line and from ground through relay 5% on the other.

As relays 28 and 42 are joined to that part of the talking circuit which is included between the condensers 22 and 79, the battery connected to these relays is without effect.

\Ve will now assume that the called subscriber was already engaged either as a calling or as a called party. if the wanted line is busy as a calling line, battery potential will be supplied to the lower terminals of the line from battery, through resistance 23 of the trunk associated with said line. If busy as a called line, battery potential will be supplied to said lower terminal from battery through the relay 67 of the trunk connected to said line. Therefore, when relay 63 retracts its armature at the end of the units series of impulses and before the armature of escapement ma net 64; is retracted, a circuit will be momentarily completed from battery through one or the other of the circuits just referred to, the lower terminal of the wanted subscribers line, and thence through brush 62, side switch wiper 66 (which will still be in second position), the right winding of test relay 60, contact and armature of magnet 6%, back contact of relay 63 to ground. Relay 60 will be energized and will lock up in series with the escapement magnet 64. This circuit may be traced from grounded battery through magnet 6%, wiper 70 and its second contact, left contact and armature of relay 60, left wind ing of said relay to ground. The retraction of the outermost right armature of relay 6O interrupts the circuit to the stepping n1agnet 65.

The innermost right armature of relay 60 completes a circuit from ground through the busy tone apparatus 71 to the upper side of the line. This will produce a distinctive tone in the receiver of the calling subscriber which will notify him that the wanted line is busy.

The release of the line finder and the selectors, shown on Fig. 2 of the drawings, is controlled solely by the calling subscriber. The release of the connector (Fig. 3) is controlled jointly by the calling and called subscribers.

It will be remembered that battery for the calling subscriber was supplied to the upper side of the talking circuit through relay 56 (Fig. 3). This relay, therefore, remained energized during conversation and caused relay 55 to be held up. We will assume that the calling subscriber is the first to place his receiver on the hook. YVhen the circuit is interrupted at the calling substation, relay 56 deenergizes and ccmpletes a momentary energizing circuit through relay 63. Relay 55 falls 06 an instant later, completing a circuit from ground through its left armature and back contact, outermost armature and contact of relay 63, front contact of relay 54 to the lower side of the talking conductor, and over the lower side of the talking circuit, through relays 42 and 28 in parallel to battery and ground. Relay 28 completes a circuit from grounded battery through release magnet 72 (Fig. 1), back contact of relay 3, side switch wiper 33 and its third contact, back contact and right armature of relay 27, and front contact of relay 28 to ground. A circuit is alsocompleted frcm battery, through release relay 44:, off-normal contact 73 to wiper 33 and thence to ground as before. Both release magnets 72 and A are energized and lock up. The locking circuit for release magnet 7 2 extends from battery through off-normal contact 7% (closed when the switch takes its first step), and its armature and front contact back to battery. A similar locking circuit is completed for magnet it. through ofi-normal contact 73, and the armature and contact of this magnet. Relay in attract ing its armature completed a circuit from ground through its armature and front contact, armature and back contact of relay 40, side switch wiper T5, now in its third position, off-normal contact 76 (closed by the switch on its first movement), and release magnet 57 to battery and ground. Release magnet 57 pulls up and an energizing circuit, similar to that described in connection vith release magnet it, is maintained therefor until it reaches its normal condition.v The energization of release magnets 722, lland 57 will return the line finder switch (Fig. 1) and the selector switches (Fig. to their normal position.

The final switch or connector (Fig. 3), however, will not be released until the called subscriber places his receiver on its hook. Upon the interruption of the substation circuit at the called subscribers line, relay 5% will retract its armature to complete a circuit from battery, through release magnet 77, off-normal contact 78, right armature and back contact of relay 5a, back contact and left armature of relay 55 to ground. (As the selectors in Fig. 2 have been returned to their normal position, line relay 56 and therefore slow relay 55 are deenergized.) Release magnet 77 is energized and. completes a locking or maintaining circuit for itself until the connector has reached its normal position, when contact 78 will be opened, allowing the armature for magnet 77 to retract.

If the called subscriber is first to replace his receiver upon the hook, relay 54 will be deenergized. This, however, will not the release of the connector switch as the release circuit will be opened at the back contact and left armature of relay ll ow, when the circuit is opened at the calling substation, relay 56 (F 3) will be decnen gized, and in falling off will interrupt the circuit of relay which retracts its armature. The left armature of relay 55 at back contact completes the hereinbefori traced circuit for the release magnet 77. A its right armature ant back contact it causes ground potential to be supplied to the lower conductor f the talking circuit from ground, through armature and back contact of relay 56, armature and back contact of relay 55, and armature and back contact of relay 5%. Relays 28 and 42 (Fig. are energized as before described. From this point on release takes place in the same man her as herebefore described.

lVe will now consider the modification of the finder switch circuit shown on Fig. 4 of the drawings. In this modification direct current is associated with the test relay 4-, and contact 19 is joined to the lower conductor of the trunk on the opposite side of the condenser 22 from the circuits of Fig. 1. In Fig. 4 the resistance 23 is connected directly to ground, and battery is associated with the cutoff relay 2 1.

The circuits of the common relays have also been slightly modified, so only one armature is required on test relays 4. It will be seen that the ground for all the operating circuits of finder switch mechanism is supplied through the back contact of test relay a and the left front contact of line relay 1. It is believed that the circuits can be readily traced from the foregoing description of the circuits of Fig. 1 taken in connection with the above explanation.

It may be here explained that upon the energization of the release magnets, the wipers of the corresponding side switches are returned to their normal positions, thus making the trunks immediately selectable. These trunks may be instantly taken in the establishment of another call even before the corresponding switches have reached their normal positions, but the release and the return to normal of the switches will not be affected by the selection of the corresponding trunks on account of the lcckin circuits for the release magnets which have been described.

The test circuits of the finder switch may be materially modified in several ways. Instead of the alternating generator 18, Fig. 1. or the battery joined to the test relay Fi l, source of pulsating current may be used. Also in place of the condenser in tle lower conductor of the trunk, a high resistance may be placed in the wire lea ling from the contact 19 to said conductor, or contact 19 may be connected directly to earth through a resistance or a condenser or through both.

Although these eXpe-dieuts are found to give fairly satisfactory results, the arrangements herein discloscl are the preferred forms of the invention.

lVhile this invention is disclosed in a system employing line finding switches, it may be readily adapted to systems employing line switches, in which case means would beprov rided to associate the test relay with the contact terminal of an idle trunk.

Many modifications of the invention. other than those enumerated, will readily suggest themselves to those skilled in the art, and the invention should therefore be limited merely by the scope of the claims.

What is claimed is:

1. in a telephone exchange system, a switch having a movable terminal and a series of fixed terminals, lines terminating in said fixed terminals, aline terminating in said movable terminal, a test relay, means for joining said test relay to the fixed terminal of any of said first mentioned lines, and means for completing the circuit of said relay upon engagement of said movable terminal with said fixed terminal.

2. In a telephone exchange system, a switch having a series of sets of fixed terminals and movable terminals arranged to traverse said fixed terminals, lines terminating in said sets of fixed terminals, a line terminating in said movable terminals, a test relay and a source of current, means for joining said relay and source of current to any of the fixed terminals of said prior to the engagement of said terminals by said movable terminals, and means for completing the circuit of said relay upon the engagement of said movable terminals with said fixed terminals.

3. In a telephone exchange system, a switch having a series ott' fixed terminals and a movable terminal arranged to traverse said fixed terminals, lines terminating in said fixed terminals, a line terminating in said movable terminals, means for automatically in ving said movable terminals over said fixed terminals, a test relay and a source of current, means actuated on the initiation of a call for joining said relay and source of current to the terminals of said first mentioned lines throughout the operation of said switch. and means for completing the circuit of said relay through the movable terminal of said switch upon the engagement of said movable terminal with the fixed terminal of said line. i

4-. In atelephone system, a pair of lines, an automatic finder switch for joining one of said lines to the other, the first one of said lines terminating in fixed contacts of said switch and the second line terminating in the movable contacts of said switch, a test relay, means actuated on the initiation of a call for joining said relay to one of the fixed terminal contacts of said first line throughout the automatic hunting operation of said switch, and means actuated upon one of said movable terminals engaging said fixed contact for stopping the movement of said switch.

In a telephone system, a subscribers line, a trunk line, an automatic finder switch for connecting said line to said trunk, terminal contacts of the talking conductors of said line at said switch, a test relay for stopping said switch, and means for temporarily joining said test relay to one of said terminal contacts during a call.

6. In a telephone system, a group of subscribers lines, a trunk line, an automatic switch for connecting said trunk to any of the lines of said group, the lines of said group terminating in fixed contacts of said first mentioned lines switch, said trunk line terminating in the movable contacts of said switch, a test relay,

means actuatedupon the initiation of a call upon one of said lines for joining said relay 1. a group of subscribers lines, a finder switch having fixed contacts in which said lines terminate, a trunk line terminating in the movable contacts of said switch, a test relay common to said group of lines, means actuated upon the initiation of a call on any one of said lines for connecting said test relay to a terminal of the calling line and for causing said switch to automatically hunt. for the terminals of said line, means for completing the circuit of said test relay upon engagement of the movable terminals of said switch with the fixed terminals of said line, and means controlled by said relay for stopping the movement of said switch.

j 8. In a telephone exchange system, a group of subscribers lines, a group of switches each having fixed contacts at which said lines terminate, movable contacts arranged to traverse said fixed contacts, a test relay common to said group or lines and to said switches for stopping any one of said switches, means for allott'ing one of said switches to make connection to a calling line, means actuated upon the initiation of a call on one of said lines for joining said test relay to a fixed terminal of said line at an allotted switch and for causing the movement of the movable terminals of said switch over the terminals of the lines of said group, and means for completing a circuit for said test relay upon the engagement of the fixed terminals of the calling line by the movable terminals of said switch.

9. In a telephone exchange System, a group of subscribers lines, a group of trunk lines, switches each having fixed terminals in which the lines of said group terminate, and movable terminals in which said trunks respectively terminate, means for causing the operation of any one of said switches to connect the corresponding trunk to a calling line, a test relay for stopping any one of said switches, and means actuated upon initiation of a call upon one of said lines for associating said relay with any one of said switches to control the operation thereof.

10. In a telephone exchange system, a plurality of groups of subscribers lines, a group of trunk lines, switches each having series of fixed terminals in which said groups of lines terminate and movable terminals at which said trunks respectively terminate, a

test relay for stopping any one of said switches common to each group of lines, means actuated on the initiation of a call on any one of said lines for causing the movable terminals of one of said switches to move over the terminals of the group of lines and for definitely associating the test relay of the group of the calling line with said switch to control the operation thereof.

11. In a telephone system, a subscribers line, a trunk line, a switch having fixed terminals in which said subscribers line terminates and movable terminals in which said trunk line terminates, a test relay and a source of current means actuating upon the initiation of a call on said subscribers line for joining said relay and source of current to a terminal of said line and for causing said switch to seek for said fixed terminal, and means for completing the circuit of said test relay upon the engagement of said fiXed terminal by said movable terminal, said test relay operating to stop the movement of said switcl 12. In a telephone system, a group or" incoming lines, a group of out oing lines, a group of switches for connecting said incoming lines to said outgoing lines, and a test relay common to said switches for stopping any one of said switches when a connection is being established to any one of said incoming lines.

13. In a telephone system, a subscribers line, finder switches and connector switch-es, to which the talking conductors of said line are multipled, and testing means whereby the multiple terminal contacts of one of said conductors are employed as test contacts of said finder switches and the multiple terminal contacts of the other said conductor are employed as test contacts at said connector switches.

is. In a telephone system, calling and called subscribers lines, a talking circuit established from the calling to the called line, a pair of condensers, a portion of said talking circuit being included between said condensers, a release relay connected to the portion of said talking circuit between said condensers, and means actuated upon interruptingthe circuit at the substation of one of said subscribers for completing a circuit for said release relay.

15. In a telephone exchange system, a calling and a called subscribefs line, a talk ing circuit established from the calling line to the called line, a portion of said talking circuit being inductively associated with but conductively removed from the rest of the talking circuit, a switch by means of which said talking circuit is established, a release relay for said switch joined to the inductively conn cted portion of said talking circuit, and means actuated upon interrupting the substation circuit at one of said lines for completing a circuit for said release relay.

16. In a telephone system, trunk lines, selector switches each having stationary contacts at which. said trunk lines terminate, means for causing a selector switch to hunt for and make connection to an idle one of said trunks, said means including a lead for impartingto the test brush of a seeking switch a certain electrical potential and leads for imparting to the test contacts of idle trunks a dit erent electrical potential, and means for imparting to the test contacts of a selected trunk a potential equal to that of the test brush of a seeking switch.

17. In a telephone system, trunk lines each comprising two talking conductors, selector switches having stationary contacts at which the conductors of each of said trunks ter minate, means for causing a selector switch to hunt for and make connection to an idle one of said trunks, said means including a lead for imparting to the test brush of the seeking switch a certain electrical potential and leads for imparting to the terminal contacts of talking conductors of idle trunks a different electrical potential, and means for imparting to the test terminals of a selected trunk a potential equal to that of the test brush of aseeking switch.

18. In a telephone system, trunk lines, each comprising two talking conductors. selector switches each having stationary contacts at which the conductors of each of said trunks terminate, means for causing a selector switch to hunt for and make connection to an idle one of said trunks, said means including a lean. for imparting to the test brush of a seeking switch a certain electrical potential and leads for imparting ta the terminal contacts of talking conductors of idle trunks a difierent electrical potential, means whereby the portion of the circuit including the test brush of a selector switch and the associated trunk terminal contact are inductively connected to but conductively separated from the rest of the circuit, and means overative upon completing a connection to a trunk for interrupting the lead normally supplying idle potential to the terminals thereof, whereby the multiple test terminals of said trunk are caused to assume a potential equal to that of the test brush of a seeking switch.

19. In a telephone system, trunk lines each comprising two talking conductors, selector switches each having stationary contacts at which the conductors of each of said trunks terminate, means for causing a selector switch to hunt for and make connection to an idle one of said trunks, said means including a lead for imparting to the test brush of a seeking switch a certain electrical potential and a lead for imparting to the terminal contacts of the corresponding talking conductors of idle trunks a different electrical potential, condensers between which the portion of the circuit including the test brush of the selector switch and the associated trunk terminal contacts are included, and means operative upon completing a connection to a trunk for interrupting the lead normally supplying idle potential to the terminal thereof, whereby the multiple test terminals of said trunks are caused to assume a potential equal to that of the test brush of a seeking switch.

20. In a telephone system, telephone circuits each comprising two talking conductors, a switch having stationary contacts at which the conductors of said circuits terminate, means for causing a switch to make connection to and test any one of said circuits, said testing means including a lead for imparting to the test brush of said switch a certain electrical potential and leads for imparting to the terminal contacts of the corresponding talking conductor of idle circuits a different electrical potential, means whereby the portion of the circuit including the test brush of said switch and the associated circuit terminal contact are inductively connected to but conductively separated from the rest of the circuit, and means operative upon completing a connection to a circuit for interrupting the lead normally supplying idle potential to the terminals thereof, whereby the multiple test terminals of said circuit are caused to assume a potential equal to that of the test brush of a seeking switch.

21. In a telephone system, a subscribers line, a trunk line, an automatic finder switch for connecting said line to said trunk, means for controlling said automatic finder switch, terminal contacts of the talking conductors of said line at said switch, a test relay temporarily connected to one of said terminal contacts, and means associated with said relay for stopping the finder switch.

22. In atelephone exchange system, a switch having a movable terminal and a series of fixed terminals, a group of incoming lines terminating in said fixed terminals, an outgoing line terminating in said movable terminal, a test relay associated with the group of incoming lines, means operative upon the initiation of a call on one of said lines of said group for starting said switch and for connecting said relay to one of the terminals of said lines at said switch, and means for completing the circuit of said relay upon engagement of said movable terminal with said fixed terminal.

23,111 a telephone exchange system, a switch having a movable terminal and a series of fixed terminals, a group of inco1n ing lines terminating in said fixed terminals, an outgoing line terminating in said movable terminal, a test relay associated with but normally disconnected from the group of incoming lines, means operative upon the initiation of a call on one of said lines of said group for starting said switch and for connecting said relay to one of the terminals of said lines at said switch, and means for completing the circuit of said relay upon engagement of said movable terminal wlth said fixed terminal.

In witness whereof I hereunto subscribe my name this 19th day of June, A. D. 1915.

CHARLES L. GOODRUM.

Copies of this patent may be obtained for five cents each, by addressing the "Commissioner 0! Patents, Washington, D. 0. 

